Structural, magnetic and magnetocaloric properties in distorted RE 2NiTiO6 double perovskite compounds

The magnetocaloric effect based Magnetic refrigeration (MR) was considered a novel energy-efficient and environmentally benign cooling method. However, the lack of suitable magnetic solids has slowed the development of its practical applications. We herein fabricated the RE _2 NiTiO _6 ( RE = Gd, Tb and Ho) double perovskite (DP) compounds and systematically determined their structural, magnetic and magnetocaloric properties by experimental determination and density functional theory calculations, in which the Gd _2 NiTiO _6 was realized to exhibit promising cryogenic magnetocaloric performances. The results indicated that all the RE _2 NiTiO _6 DP compounds crystallized in a distorted monoclinic structure with P 2 _1 / n space group and underwent a second order type magnetic phase transition around 4.3, 4.5 and 3.9 K, for Gd _2 NiTiO _6 , Tb _2 NiTiO _6 and Ho _2 NiTiO _6 , respectively. The magnetocaloric performances were checked by the parameters of maximum magnetic entropy change and relative cooling power, which are 31.28 J·kg ^−1 ·K ^−1 and 242.11 J·kg ^−1 for Gd _2 NiTiO _6 , 13.08 J·kg ^−1 ·K ^−1 and 213.41 J·kg ^−1 for Tb _2 NiTiO _6 , 11.98 J·kg ^−1 ·K ^−1 and 221.73 J·kg ^−1 for Ho _2 NiTiO _6 under the magnetic field change of 0–50 kOe, respectively. Evidently, the Gd _2 NiTiO _6 compound exhibit promising magnetocaloric performances and therefore is of potential for practical cryogenic MR applications

<p>Magnetic properties and giant cryogenic magnetocaloric effect in B-site ordered antiferromagnetic Gd2MgTiO6 double perovskite oxide</p>

The magnetic refrigeration (MR) technology by utilizing the magnetocaloric (MC) effects of magnetic solids have been realized to be a promising energy efficiency and environmentally friendly technology. Developing or discovering proper magnetic solids with promising MC performances is one of the most important tasks at present stage since a huge gap still exists between the requirement of practical MR application and the MC performances of the magnetic solids. Herein, we reported a combined theoretical and experimental investigation of the crystal structure together with the magnetic properties, magnetic phase transition (MPT) and MC performances in Gd2MgTiO6 oxide. The Gd2MgTiO6 is confirmed to crystalize in a B-site ordered monoclinic double perovskite (DP) crystal structure. A rather unstable anti ferromagnetic (AFM) interaction with large magnetic moment and semi-conductor characteristic with the band gap of 2.977 eV have been confirmed in Gd2MgTiO6 DP oxide at ground state. Giant reversible cryogenic MC effect together with excellent MC performances have been confirmed by a series of the figure of merits including the values of maximum magnetic entropy change (-delta S-M) and refrigerant capacity ( RC ), which are evaluated to be 46.21 J/kgK and 300.27 J/kg around 3.3 K with the magnetic change of 0-7 T, these values are much better than most of the recently reported famous cryogenic MC materials and the commercialized magnetic refrigerants gadolinium gallium garnet (GGG) as well. The observed excellent MC performances suggest that Gd2MgTiO6 DP oxide is a promising candidate material for cryogenic MR applications. (C)& nbsp;2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved